Wiggins gasholders and the like are generally known in the art as apparatus for recovering and storing gas. Such gasholders are provided with a tank for storing gas, a movable piston that rises and falls within the tank, a shock-absorbing member that rises and falls within the tank along with the movable piston, and cylindrical sealing members that connect the tank to the shock-absorbing member and the shock-absorbing member to the movable piston. These sealing members are formed from chloroprene rubber, acrylonitrile butadiene rubber, or the like (see, for example, Japanese Unexamined Patent Application Publication Nos. 2001-271994A and 2003-113366A).
Of these two cylindrical sealing members, the sealing member disposed between the tank and the shock-absorbing member has one end anchored to an inner circumferential surface of the tank and the other end anchored to an outer edge of the shock-absorbing member. Thus, the areas near the one end (tank-ward end) and the other end (shock-absorbing member-ward end) of the sealing member are constantly in a bent state, with this bent state varying with the vertical movement of the movable piston and shock-absorbing member. Thus, in addition to superior gas-tightness so as to prevent the stored gas from leaking, bending resistance is demanded for the sealing member.
However, when a gasholder is installed in a cold region, the sealing member may be cooled to near the brittleness point of the rubber. In particular, the tank-ward end of the sealing member tends to transmit the low temperature of the outside air via the wall faces of the tank. A sealing member formed from chloroprene rubber or acrylonitrile butadiene rubber will exhibit inferior cold resistance, leading to the problem that cracks are readily formed in the member at low temperatures in cold regions even if no cracks are formed in the bent section at normal temperatures. On the other hand, a sealing member formed from a rubber other than chloroprene rubber or acrylonitrile butadiene rubber will exhibit inferior durability (gas resistance) against methane gas and the like, leading to the problem that the fundamental function of the sealing member is inhibited.